1. Field of the Invention
The present invention relates generally to a magnetic head core and a method for producing the same, and more particularly to a magnetic head core suitable for a video tape recorder (VTR) and a floppy disk drive (FDD), and a method for producing such VTR and FDD magnetic head cores.
2. Discussion of the Prior Art
In the art of information storage and retrieval by a floppy disk drive (FDD), there is a tendency toward high-density storage of information on a memory medium, for increasing the storage capacity of the memory medium. This tendency caused a bulk type magnetic head to become predominant in the art. A typical construction of such a bulk type magnetic head is disclosed in laid-open Publication No. 59-227019 of unexamined Japanese Patent Application. As shown in FIG. 1(b), this type of magnetic head has a writing/reading core 2 and an erasing core 4, which are bonded together with their backs butted together, such that magnetic gaps 2a, 4a of the cores 2, 4 maintain a predetermined relative position in the direction perpendicular to the direction in which the writing/reading and erasing tracks extend across the gaps 2a, 4a.
Described in detail, a pair of ferrite blocks are prepared for the writing/reading core 2, such that a groove is formed in each of the abutting surfaces of the two blocks, so as to define the width of the writing/reading track. The groove is filled with a glass material. The portion of the glass filler which are located outside the groove is removed, and the areas of the abutting surfaces at which the two ferrite blocks are bonded together are mirror-polished. Then, a groove for defining the depth of the writing/reading magnetic gap is formed in one of the ferrite blocks. Subsequently, the mirror polished areas of at least one of the abutting surfaces of the two blocks are coated with spacer layers having a suitable thickness, and the gap depth defining groove is filled with a glass material, so that the two ferrite blocks are bonded together by the glass. Thus, a ferrite core block for the writing/reading core 2 is prepared. The erasing core 4 is prepared in the same manner as the writing/reading core 2 described above.
The ferrite core blocks for giving the writing/reading and erasing cores 2, 4 are butted together at their backs, such that the writing/reading tracks and the erasing tracks are properly positioned relative to each other in the direction perpendicular to the direction of extension of the tracks. The core blocks are bonded together with a glass or resin, into an integral ferrite structure. Suitably shaped grooves are cut in the prepared ferrite structure, so as to provide leg portions. Subsequently, the ferrite structure is cut into two or more FDD composite magnetic head cores, each of which has the writing/reading core 2 and the erasing core 4, as shown in FIG. 1(b).
In the known method described above, two grooving operations for defining the width of the tracks are required for each of the core blocks for the writing/reading and erasing cores 2, 4. In addition, a further grooving operation is required for defining the depth of the magnetic gaps, for each of the core blocks. Also, bonding operations should be effected three times, i.e., the first bonding of the ferrite blocks to prepare the core block for the writing/reading core 2, the second bonding of the ferrite blocks to prepare the core block for the erasing core 4, and the third bonding of the two core blocks to prepare the integral core structure. Thus, the known method requires a comparatively large number of process steps, and the produced magnetic head core is relatively expensive.
Another drawback of the known composite magnetic head core is derived from the bonding of the two core blocks with the track defining grooves which have been formed independently of each other. Namely, the two core blocks should be positioned relative to each other when the core blocks are bonded together, with the writing/reading and erasing magnetic gaps separated from each other by the two inner abutting ferrite blocks. Accordingly, it is considerably difficult to establish sufficiently high accuracy of relative alignment of the writing/reading tracks and the erasing tracks.
Also known in the art is a magnetic head core having a single writing/reading core, as disclosed in laid-open Publication No. 57-4005 of examined Japanese Patent Application. According to the disclosure, the writing/reading track and the corresponding magnetic gap are formed by etching at least one of two ferrite blocks, through a pattern of etching masks applied to the ferrite block or blocks. However, this publication does not show a manner of producing a composite magnetic head core, by etching a ferrite block or blocks.